release-kit 0.2.9

A canonical release workflow: a technology-agnostic method, per-technology bindings, and the rk CLI that lands and serves them.
Documentation
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- This project works in worktrees: every code-changing branch lives in its linked worktree (`rk worktree add <branch>` creates or adopts it beside the checkout), the main checkout commits nothing, and `rk worktree prune` retires a merged worktree. One branch, one writer.